Performance of Microwave Treatment of Cephalosporin Mycelial Dreg (CMD) for Utilization as Fertilizer

Author:Cai Chen

Supervisor:liu hui ling wang peng


Degree Year:2018





Antibiotic-producing mycelial dreg(AMD)is a byproduct of the fermentative process after recovering antibiotics from antibiotic-producing manufacturers.Recently,more than 2 million tonnes of raw AMD is generated each year in China.Without immediate disposal,raw AMD may lead to air,water and soil pollutions due to the high moisture(90%),and could exacerbate the spread of antibiotic resistance genes(ARG),potentially threatening public health.AMD has been categorized into hazardous waste lists for China since 2008,significantly preventing from long-term development of the antibiotic-producing industry.Cephalosporins contribute to the largest antibiotic market share in China,thus implying the highest percentage of cephalosporin mycelial dreg(CMD)among the total amount of AMD.Considering the rich nutrients contained in CMD and the instability of residual antibiotics,the objectives of this study are to establish a new route combing the harmless technology of CMD using microwave irradiation with subsequent utilization as a fertilizer;and evaluate the environmental benefits and potential risks including the ARG pollution.This study firstly investigated the performance of harmless treatment using microwave irradiation for the break of mycelial cell wall and degradation of residual cephalosporin antibiotics as well as the release of fertilizer-use organic matters.The results reveal that microwave heating temperature significantly affects the efficacy of harmless treatment for CMD.Microwave irradiation improves the CMD solubilization(3%),breaks up the mycelial cell walls,releases more fertilizer-use organic matters(77%-148%).Up to 99.9%of the residual antibiotics in CMD are degraded by microwave irradiation without antibacterial activities that are proven by the possible degradation pathway we elucidate,reducing the environmental risks.The reaction parameters of harmless treatment were optimized(initial mositrue content of CMD is 90%,effiectly reaching the temperature of 100?C under microwave power of 700 W,thereafter adjusting to the constent temperature model for more than 15 min).We also investigated the effects of microwave irradiation on the CMD dewaterability and explored the potential mechanisms.The results indicate that the reaction time and heating temperature significantly impacted the CMD dewaterability,and two dewaterability parameters presented different patterns.Capillary suction time measurements initially increased and later decreased,while water content of CMD cake values substantially increased.Microwave irradiation heavily influences the released of extracellular polymeric substances and CMD particle size,which are significantly correlated to CMD dewaterability(R2>0.90,P<0.01).However,bound water in the matrix was not destroyed and the dp90index declined by 48.2%-63.9%.The air-drying properties of CMD cake weakened(3 h)after microwave irradiation.Taken together,microwave treatment may not enhance the dewaterability or the air-drying properties of CMD.To utilize the irradiated CMD as fertilizer,this study evaluated the evolution profiles of fluorescent substances and the consequent environmental risks following the application of CMD to the soil.The specific fluorescent peak related to protein-like substances gradually disappeared,while those related to humic acid-like substances continued to increase thereafter with two new peaks in the region V.Fluorescence regional integration(FRI)results showed an increased value of 93.4%in the region V and an ascended PV,n/PIII,n index(1.94).In addition,during the ageing period,the CMD-treated soil experienced a rise in soil pH and soil electrical conductivity,along with a substantial decline in soil organic carbon and soil organic nitrogen content which significantly correlated with fluorescent data(M2=0.2875,r=0.8441,P<0.001,999 permutations for Procrustes analysis).The CMD treatment could not increase the heavy metal contents in soil.The persistence of antibiotics that may be potentially introduced into the soil by CMD treatment is relatively low(0.3-0.8 d).The initial phytotoxic effects disappeared at the end of the incubation period.To investigate the effects of CMD amendment on the soil ARGs,the structural equation modeling(SEM)was developed.Results showed that raw-CMD amendment of soil increased the detected numbers ofβ-lactam resistance genes and lateral gene transfer ability by 2 fold,while the irradiated CMD by harmless treatment failed to induce the development of new ARGs and to increase the potential of ARG transfer in the soil.Marked shifts in the native soil bacterial composition were observed and taxa of the Bacteroidetes,Actinobacteria,Proteobacteria and Firmicutes contained the greatest proportion of resistance genes.Additionally,soil properties and antibiotics or metabolites contained in raw CMD contributed to the selection of resistant microorganisms.These results imply a supplement of safey assessment using ARGs when application of CMD to the arable soil,which provides a reference of technical specification for pollution control in the pharmacetucial industry.